"I also understand that the moon face (and fat in other areas I assume) goes away after you stop taking prednisone.
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I think it depends on how long you are on prednisone. I didn't develop an obvious moon face but I certainly gained weight. For the longest time I would tell people I was gaining weight but they assured me that I "carried the extra weight well." I wasn't too concerned about the extra weight because I thought it would be easy for me to lose it again as soon as I could stop Prednisone and when I could resume my exercise routine again.

Five years after discontinuing prednisone I still struggle to lose my prednisone weight. Most of my weight used to be muscle weight. My problem with prednisone was muscle wasting. Google artificial intelligence spells it out more concisely than I can:

"Muscle wasting, also known as muscle atrophy, is a significant side effect of taking prednisone (a glucocorticoid steroid) and can contribute to the development of metabolic syndrome, which is characterized by a cluster of health issues including increased waist circumference, high blood pressure, high cholesterol, and high blood sugar; essentially, prednisone can cause muscle breakdown while promoting fat accumulation, leading to metabolic imbalances."

I still see an endocrinologist for metabolic syndrome. He forewarned me that some of my prednisone side effects might be irreversible. With diet and exercise I have reversed everything except the extra weight. Now I can blame Actemra for my extra weight but I'm just making excuses for all the prednisone weight that I gained.